Yes, this is a difficult one to hear - I should have done the ping-pong delay instead, in hindsight.

To hear this one, you need a WAV file that has material in one channel, then the other. I used a WAV file that had single snare hits in the left channel, then some silence, then hits in the right channel. You need that silent gap to hear the feedback crossing back and forth. This algorithm came from the Korg Wavestation; I think maybe synth patches (or arpeggiated things) work better with that one. If you have the Synth book, the last chapter is a set of delay FX including ping pong and a couple of multitap delays that bounce stuff back and forth between the speakers really nicely.

You can also use the ping-pong block diagram in the FX book, but you need to make the L and R delays have different lengths to hear the effect - other wise, it's difficult to hear. You can also try this on the cross-delay; let the user adjust a ratio control that sets the L and R delays as multiples of one another.

- Will